I am right-handed which probably lends itself to my natural right side. I don't really think it matters too much which side you unclip when rolling to a stop as long as you are comfortable with it. I think the concept of unclipping on the side of the road you drive on comes from the idea that if you fall off on when unclipping you do not want to risk spilling out into oncoming traffic. Also if you are riding in the city with curbs it gives you a place to put your foot on. I have attached a link to one of the videos on unclipping from GCN. All in, the best practice is what comes naturally to you and works.